The present invention relates to composite membranes and methods of making composite membranes. The membranes provided by the present invention display performance enhancements relative to conventional composite membranes.
A wide variety of thin film composite membranes are known and have been found useful in the purification of fluids comprising solutes, for example the removal of salt from sea water to provide potable water. Typically, such thin film composite membranes are prepared by performing an interfacial polymerization of a polyacid chloride in a water immiscible organic solvent with a polyamine in an aqueous solution on a surface of a porous base membrane. The resultant polyamide is deposited as a thin film on one surface of the porous base membrane. Such membranes are often referred to as composite membranes because of the presence of at least two layers in the membrane structure, which are the porous base membrane and the interfacially prepared polyamide film layer. Composite membrane performance characteristics have been shown to vary depending on the structure of the polyamide layer and the presence of or absence of additives in the interfacial polymerization reaction mixture. In addition, such thin film composite membranes are sensitive to the effects of water under pressure experienced as water is forced through the membrane. For example, pressure induced compaction of the polyamide film at the surface of the porous base membrane can lead to lower porosity over time and loss of membrane performance.
Despite the technical excellence of many recent advances in composite membrane technology, improvements are still being sought in light of the growing demands on the world's water supplies. There is a need for improved membranes that have a combination of high selectivity, flux and chemical tolerance in addition to being efficient and economical. Further there is a need for new membrane compositions and methods that can provide membranes having such superior performance characteristics.